TRENDS IN 2,3,7,8-TCDD CONCENTRATIONS IN FISH-TISSUES DOWNSTREAM OF PULP-MILLS BLEACHING WITH CHLORINE

Field measurements of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) conce ntrations in tissues from riverine environments impacted by treated pu lp and paper industry effluent in the United States were analyzed. Dat a from 39 sites in 14 states across the four major U.S. paper-making r egions were assembled and analyzed to determine the annual change in l ipid-normalized concentrations of TCDD in fish tissue. The results pro vide strong evidence of a nationwide trend of decreasing lipid-normali zed TCDD concentrations in fish tissue, with 84% of the examined sites showing a decrease. While the paucity of data currently limits any co nclusions regarding the statistical significance at individual sites, the overall median rate calculated indicates a 0.36 annual fractional decrease in lipid-normalized concentrations of TCDD in fish tissue (0. 18 to 0.51, 95% confidence interval); the average annual fractional de crease was 0.35 (0.23 to 0.47, 95% confidence interval). Subdividing f ish into benthic and nonbenthic categories resulted in rates which wer e not significantly different from one another for both the median and mean statistics.